Waterproofing an already-built pool: a step-by-step guide

Having a pool at home means much more than having a place to cool off; it is a refuge of calm and togetherness that adds incalculable value to your home. 

However, for that peace of mind to be real, the structure must function with clockwork precision. 

Water has remarkable persistence and, without an impenetrable barrier, it will eventually find the smallest crack through which to make its way. 

Learning how to professionally waterproof a pool by applying the waterproofing product Proper waterproofing is not only a matter of technical maintenance, but also the best guarantee that your investment and moments of relaxation will not be interrupted by avoidable problems.

The Physics of Water and Its Determination to Escape

You may have wondered why damp patches appear if the concrete seems like solid rock. 

The reality is that water exerts constant pressure on every centimeter of the walls and floor, looking for any weakness through which to seep.

• The Nature of Concrete: Although it appears compact at first glance, this material is porous by definition. If it is not treated properly, moisture travels through its microchannels and may reach the steel reinforcement. When the metal rusts, it expands and eventually breaks the structure from the inside.
• The Highest-Risk Areas: Most problems do not originate on smooth surfaces, but at the joints. Fixtures such as lights, skimmers, and return nozzles are critical points where the seal often fails if sufficient care is not taken when waterproofing the pool.
• The Invisible Movement: temperature changes cause the materials to constantly expand and contract. If the waterproofing is not flexible enough to accommodate these movements, those small cracks that cause so much concern will eventually appear.

What Happens If You Let Time Pass

It is human nature to try to ignore a small drop in the water level, thinking it may be evaporation, but postponing the decision to waterproof an already-built pool usually proves costly. 

The consequences of a leak go far beyond a water bill that is somewhat higher than usual.

The Silent Drain on Your Budget

When your pool loses water, you also lose the money invested in the chemical treatments and pool products necessary for its maintenance. 

Every time you refill the pool to compensate for the leak, you dilute the chlorine and pH regulators, forcing you to spend more to keep the water crystal clear and safe for swimming. 

Additionally, that escaping water has to go somewhere; it often accumulates beneath the ground, potentially eroding the terrain and compromising the stability of nearby terraces or walls.

The importance of a sound finish

A pool shell that leaks water will often end up expelling the tiles or ceramic material covering it. 

The pressure from inside the wall eventually causes the pieces to come loose, turning a watertightness problem into an aesthetic disaster. 

When it is time to take action on your pool

Identifying the precise moment to intervene in your pool makes the difference between preventive maintenance and a major renovation. 

Often, the signs indicating the need to waterproof an existing pool do not appear dramatically, but through subtle changes that, if you learn to observe them, will allow you to protect the structure before the damage becomes severe. 

It is not only a matter of monitoring whether the water level drops, but also of understanding how your pool shell withstands the passage of time and external elements.

Visual signs you should not overlook

There are very clear indicators in the finish and surrounding area that warn you when watertightness has been compromised. 

If you notice any of these symptoms, you will very likely need to consider how to waterproof a pool to restore its structural and visual integrity.

• Abnormal drop in water level: although evaporation is a natural process, especially during the warmer months, a drop of more than two or three centimeters per week is usually the first warning of a real leak.
• Detached tiles: if the small ceramic pieces begin to fall off or make a hollow sound when touched, this indicates that water has penetrated behind them, degrading the bonding material.
• Emerging cracks and fissures: any fracture line, however fine it may seem, acts as a direct route for water to reach the heart of the concrete.
• Stains and efflorescence: the appearance of whitish deposits in the joints or areas of persistent dampness on the outer walls of the pool shell confirms that water is seeping through by capillary action.

The bucket test: a simple way to clear up your doubts

Before deciding to waterproof the pool, it is advisable to rule out the possibility that the water loss is simply due to the action of the sun or wind. 

There is a very reliable method you can carry out yourself without the need for complex measuring tools, simply based on direct observation.

Fill a bucket with water from the pool itself and place it on one of the steps of the access ladder, partially submerging it so that the water in both containers remains at the same temperature. 

Mark the exact level inside the bucket with tape, as well as the outside level on the pool wall. After leaving the pool unused for 24 or 48 hours, compare both marks. 

If the pool level has dropped significantly more than the level inside the bucket, you can be certain that there is a leak, and it is time to look for a definitive solution.

Understanding the source of the problem to choose the solution

Not all water losses have the same cause or require the same treatment. It is vital to distinguish the root cause of the failure so that, when waterproofing an existing pool, the result is truly long-lasting.

Wear in joints and coatings

Sometimes the concrete structure is in perfect condition, but the material sealing the joints or the ceramic coating has reached the end of its service life. In these cases, moisture slowly penetrates and causes cosmetic damage. 

The solution usually involves thorough cleaning and the application of waterproofing mortar that restores surface watertightness.

Structural movements and settlement

If your pool has undergone slight movements due to ground settlement, cracks may appear that run through the entire wall. 

A superficial patch is not enough here; you need to know how to waterproof a swimming pool using materials with a high elongation capacity, such as injection resins or technical membranes that can absorb these movements without breaking again.

Failures in embedded fittings

Sometimes the pool shell is watertight, but water escapes through the joint between the concrete and the plastic or metal elements; in these cases, the choice of sealants and adhesives highly elastic materials are the key to stopping the leak.

A very useful trick is to observe whether the water level stops exactly upon reaching the lower part of one of these fittings; if so, you will have located precisely where the waterproofing has failed.

Technical principles for understanding how to protect your pool

Understanding the physical concepts that govern the behavior of water is the first step toward ensuring that any repair in your home is a lasting success. 

It is not simply a matter of applying layers of product one after another; the goal is to create an integrated system capable of withstanding mechanical stresses and chemical attacks from the surrounding environment. 

When considering how to waterproof a swimming pool, it is very useful to visualize the pool shell as a living organism that expands, contracts, and supports tons of weight without rest. 

Only with this technical approach will you achieve true watertightness that does not depend on temporary solutions.

The difference between structural and surface protection

In aquatic construction, it is useful to distinguish between the structure that supports the weight and the barrier that protects it from the outside.

• Primary waterproofing: It is carried out during the construction phase of the pool shell. It generally consists of adding water-repellent additives directly to the concrete mix to reduce its natural porosity.
• Secondary waterproofing: is the barrier applied afterward to the finished surface. This step is vital when you need to waterproof an already-built pool, as it creates a continuous membrane that prevents water from coming into contact with the concrete, thereby avoiding reinforcement corrosion and unwanted leaks.

Water-repellent materials versus elastic membranes

Choosing the right material will always depend on the current condition of your installation. Not all products perform the same way or offer the same guarantees over the years.

Sealing mortars and additives

These products work by sealing the material’s pores. They are excellent for stopping moisture in very rigid structures, but they have one major limitation: their lack of flexibility. 

If your pool experiences even the slightest movement, these materials may crack because they cannot adapt to the new shape of the substrate.

Next-generation elastic membranes

They are the preferred option when looking for a way to waterproof a pool with the peace of mind that the solution will last. 

They can bridge microcracks; in other words, if the pool shell moves slightly due to temperature changes, the membrane stretches without breaking. 

It is the most advanced technical solution for absorbing the thermal expansion that occurs every summer.

The interplay of positive and negative pressure

This concept is often what makes the difference between a job well done and one that fails within a few months.

• Positive pressure: is exerted by water from the inside toward the walls. It is the easiest to manage, since the weight of the water itself presses the waterproofing material against the wall, helping it stay in place.
• Negative pressure: External pressure, caused by irrigation or the water table, pushes inward, attempting to detach the coating. A robust waterproofing system must withstand this pressure to prevent blistering or delamination of the finish.

The challenge of capillary action

Concrete, by its nature, can behave like a sponge. If there is an entry point, water will rise through the material’s pores, potentially causing damage in areas that are not even submerged, such as the edges or coping stones. 

For this reason, any strategy for waterproofing a pool must include a watertight seal around the entire perimeter, ensuring complete protection from top to bottom.

The step-by-step guide to bringing your pool back to life

Addressing the renovation of a pool that is losing water requires a methodical approach and absolute respect for each material’s curing times. 

If you find yourself needing to waterproof an already-built pool, success will depend not only on the quality of the product you choose, but also on how rigorously you prepare the surface before starting. 

The goal is to create a perfect bond between the old substrate and the new protective barrier, eliminating any weak point through which water could try to escape again.

Preparing the substrate: the key to adhesion

The working surface must be spotless. Dirt or chemical residues prevent the treatment from adhering, which would ruin the repair in the medium term.

• Thorough cleaning: use a pressure washer to spray water under pressure and effectively remove limescale and microorganisms. In older pools, washing with a highly diluted acidic solution helps open the material's pores, making it easier for sealing products to penetrate.
• Repairing weak areas: if the mosaic tiles are loose or the mortar crumbles to the touch, you must remove it using hand tools suitable tools until you achieve a solid, firm base. You cannot build a lasting solution on a foundation that has lost its integrity.
• Moisture control: although many technical materials can be applied to slightly damp surfaces, always avoid applying products over puddles. To work comfortably, pour the material into a paint tray clean; the balance during drying is what ensures that the waterproofing chemical works as it should.

Special attention to critical points

Before dealing with the walls and floor, you must focus your attention on the elements that interrupt the continuity of the pool shell. 

This is precisely where most attempts fail when looking for ways to waterproof a pool at home.

Sealing accessories and joints

Skimmers, lights, and nozzles are usually made of plastic or metal, which do not naturally adhere to concrete. This connection is the place most prone to leaks. 

It is necessary to clean the perimeters of these accessories thoroughly and use joint sealants specific products, such as highly elastic polyurethane sealants, that ensure watertightness despite vibrations or temperature changes.

Treatment of structural cracks

If you have found cracks, it is not enough to cover them cosmetically. You must widen them slightly into a V-shape, clean them, and fill them with repair mortars that do not shrink as they dry. 

For expansion joints, it is best to use specific elastic bands that allow the pool to “breathe” and move without the protection breaking.

Application of the waterproofing system

With the delicate areas already reinforced, it is time to apply the main protection. The most effective technique when considering how to waterproof a pool with professional finishes is the cross-layer system.

• The first coat and reinforcement: Spread the product evenly over the entire surface. While this coat is still fresh, place an alkali-resistant fiberglass mesh. This mesh will act as the skeleton of your new pool, distributing stresses and preventing small cracks in the old concrete from showing through on the surface.
• The second coat: After allowing the drying time, which usually ranges from a few hours to a full day, apply a second coat perpendicular to the first. This crosshatch application ensures that not a single pore remains open and that the thickness is ideal for withstanding the pressure of the water.

The value of patience: curing and filling

The temptation to see the pool full as soon as possible is strong, but patience will be your best ally now. A very common mistake when waterproofing a pool is filling it before the materials have completed their chemical curing process.

It is usual to wait at least one week before adding water, always depending on whether the climate is drier or more humid. 

Once this time has passed, fill the pool gradually and monitor the water level during the first few days. By following this procedure, you will be able to enjoy your pool again, confident that the shell is finally completely watertight and safe.

The materials that guarantee the success of your renovation

Choosing the right material is probably the most important technical decision you will make. 

There is no miracle product that works in every situation; the needs of a pool shell with slight structural movement are very different from those of a pool with only surface porosity. 

When deciding how to waterproof a pool, it is vital to assess your budget, but also its compatibility with the final finish and the climate in your area. 

Flexible cementitious mortars: the balance between cost and effectiveness

This material has become the preferred solution for waterproofing an existing pool because of its versatility. 

It is a high-strength cement-based compound enriched with synthetic resins that give it surprising flexibility.

• Ability to adapt: Its great advantage is that it can absorb small cracks without breaking, which is vital in concrete structures that expand and contract with heat.
• Total adhesion: It chemically bonds with the existing substrate, creating a smooth, even surface that is perfect for installing mosaic tiles or ceramic tiles afterward.
• It allows the pool shell to breathe: Although it does not let water through, it does allow vapor to escape, preventing bubbles or flaking caused by moisture accumulating behind the walls.

PVC sheet membrane: watertightness and design in one step

If you are looking for a solution that combines watertightness and design, the reinforced membrane is the most robust option. It consists of two layers of PVC reinforced with a polyester mesh, creating a flexible "bag" independent of the structure.

It is the ideal alternative for waterproofing a pool when significant cracks are present, because if the concrete moves, the membrane will not break. 

As heat welding is required to join the pieces, its installation guarantees a permanent seal and superior resistance over time.

Polyurethane resins: cutting-edge technology underwater

Liquid resins are advanced solutions applied similarly to paint, but when they dry, they create a continuous elastic waterproofing membrane, without a single joint through which water could seep.

• Extreme flexibility: polyurethane offers very high elasticity and performs wonderfully against both sunlight and chemicals in the water. It is the ideal choice for anyone looking for how to waterproof a pool with a smooth, modern finish that is very easy to clean.
• Strength and durability: with no cuts or overlaps, the risk of mechanical failures is drastically reduced, offering a pleasant feel and a cutting-edge appearance.

The role of paints: reality or temporary relief?

Chlorinated rubber paint is commonly used to save money, but it is important to be clear: it is not a definitive solution for leaks. Rather, it acts as a decorative finish with surface protection.

If the pool shell is losing water, painting will not solve the problem, as it lacks the thickness and elasticity needed to seal cracks under pressure. When waterproofing a pool, use waterproofing paint only if the structure is already watertight and you simply want to renew its appearance.

Epoxy resins for maximum protection

Epoxy resins stand out for their extreme hardness and complete resistance to osmosis. They are commonly used in fiberglass pools or installations requiring impeccable hygiene, such as saltwater pools or therapeutic facilities. 

When considering how to waterproof a pool with this material, keep in mind that its application requires the substrate to be completely dry, but the result is a glass-like surface with extraordinary durability that will withstand the passage of time without changing.

Your pool, always ready with Brikum’s support

At this point, it is clear that keeping a pool shell in optimal condition requires both careful observation and meticulous technical execution. 

At Brikum, we understand that your home is a living project, a space that evolves with you, and that the success of any improvement lies in combining the best building materials with the right knowledge. 

When deciding how to waterproof a pool, you are not just solving a technical leakage problem; you are protecting your property and ensuring that your summers remain focused on relaxation, far from concerns about dampness or unexpected drops in water level.

Final steps for a professional result

Before considering the task complete, it is worth reviewing a short checklist.

• Checking adhesion: make sure the new material has bonded perfectly with the old substrate, with no gaps or air bubbles.
• Checking the critical points: take one last look at the sealing around the lights, skimmers, and nozzles. These elements should have been integrated with flexible products that can withstand water pressure.
• The value of waiting: Patience is the final step of the process. Filling the pool before the material has completely dried and hardened is the most common mistake, and also the one that causes the most failures when waterproofing a pool.

Why trust Brikum's experience

Our experience in the DIY sector has taught us that, when it comes to containing the force of water, there is no room for shortcuts. 

At Brikum, we select only products that have proven their worth against pressure and the passage of time.

Advice tailored to your needs

We know that every pool has its own particularities. Sometimes questions arise about which mesh to choose or which mortar is best suited to your type of ground. 

Understanding how to waterproof a pool effectively also means knowing how to combine the right products; that is why having our support will help you avoid unnecessary expenses and work with complete peace of mind.

Logistics designed to match your pace

When you set out to waterproof an existing pool, time is often a key factor. 

Keeping an up-to-date stock of resins, flexible mortars, and quality tools allows us to send you what you need quickly, so your plans do not suffer delays and you can open your pool for the swimming season on time.

The peace of mind that comes from doing things right

A watertight pool is also a more sustainable pool. By eliminating leaks, you save on your water bill and reduce your use of chemical products, contributing to a more balanced environment. 

At Brikum, we want to support you every step of the way, giving you the tools and the confidence to feel proud of the final result.

With all this information about how to waterproof a pool at your fingertips, the next step is to assess what your installation needs and get to work. 

With the right materials, careful attention to detail, and respect for drying times, your pool will once again become that joyful, relaxing corner you enjoy so much.